Aluminum alloy



Patented Feb. 19, 1952 UNITED STATE ALUMINUM ALLOY Harold ErnestGresham, Little Eaton, and Douglas Wilson Hall, West Monkseaton,England, assignors to Rolls-Royce Limited, Derby, England No Drawing.Application February 4,1947, Se-

rial No. 726,440. In Great Britain February 8,

It is well known that artificially aged aluminium alloys when subjectedto severe corrosion conditions such as salt water, mist or spray, arevery prone to intercrystalline attack.

In order to avoid this corrosion effect high strength aluminium alloyssuch as Duralumin are coated with pure aluminium to give such materialsas "Alclad.

Alloys are also used of aluminium with up to 3.5 per cent of magnesiumand sometimes small additions of manganese. These alloys are of lowstrength but have high resistance to corrosion. They are however notsusceptible to artificial age hardening unless other elements are added,and the elements hitherto added for this purpose have destroyed thecorrosion resisting properties of the alloy.

We have found that the addition of silver 0.2 to 2% to an aluminiumalloy containin 1 to 3.5% magnesium gives an alloy which responds toartificial ageing, moreover this alloy is equal to or more resistant tocorrosion than the plain magnesium aluminium alloy. As a result of thisartificial ageing the alloy is also stronger than the plain alloy.

The alloy preferably contains manganese and is of the followingcomposition:

Per cent Magnesium 1 to 3.5 Silver 0.20 to 2.0 Manganese 0.05 to 1.0

Aluminium the remainder Other elements can be present in limitedamounts.

Silicon which is an impurity in aluminium should not exceed 0.35 percent and is preferably kept as low as possible.

Nickel can be present up to 2.0 per cent. Iron,

zinc, cobalt and zirconium may be present up to 1 per cent of eachwithout seriously afiecting the alloy.

Antimony, tin, chromium, may be present up to 0.5 per cent of each.

Copper, titanium, beryllium, vanadium, molybdenum, tungsten, niobium,cerium and the rare earth elements may be used as cleaners and grainrefiners upto a total of 1 per cent but with not more than 0.3 per centof any individual element. For the rare earths Misch metal may be usedand may be present up to 1.0 per cent. Other elements such as lithium,cadmium, calcium, strontium, barium, thorium, arsenic, lead, bismuth andothers may be tolerated up to 0.1 per cent individually and 0.3 per centtotal.

1 Claim. (01. 75-147) The preferred heattreatment is to give solutionheat treatment at 520 to 550 C. for. 1 to 20 hours, to quench in Waterand age at C. to 200 C. for 8 to 30 hours.

Aluminium the remainder was hot forged, solution heat treated at 550 C.for 2 hours quenched in water and aged for 24 hours at C. It gave atensile strength of 18.5 tons per square inch with 22 per centelongation. The rise in Brinell hardness which occurred as a result ofthe artificial agein was 40 points Brinell, i. e. it rose from 45 to 85Brinell. Without the silver addition it would have remained at about 45Brinell.

A well known widely used aluminium alloy containing 3.5 per centmagnesium, 0.5 per cent manganese, 0.25 per cent iron and 0.20 per centsilicon cast in the same mould and hot forged in the same manner wascorrosion tested along with the new alloy.

The results before and after nine weeks intensive corrosion in sea waterare as follows:

New Alloy Well-known Alloy Tensile Tensile Strength Elong' StrengthElong Tons Per Cent Tone Per Cent Before Corrosion 18.6 22 l7 18 AfterCorrosion 16.3 l7 l3 7. 5

Tensile strength Elongation Tom Per cent Before Corrosion 19.2 20 AfterCorrosion l7. 0 12 It will be observed this alloy is also superior tothe well known alloy.

The alloy can be used either as castings or as forgings, being heattreated in either case to suit requirements. With forgings cold work maybe introduced as a means of strengthening the alloy and may be carriedout either after solution heat treatment and before ageing, or after thefull heat treatment.

This alloy is also good for welding.

What we claim is:

An age hardened aluminum base alloy resistant to severe corrosionconditions and comprising an aluminum base alloy consisting of94.5-98.8% aluminum, 1-3.5% magnesium and 0.20-2.0% silver in thecondition produced by solution heat treatment of 1-20 hours at 520-550(3., followed by quenching and 8-30 hours agein at 160-200" C.

HAROLD ERNEST GRESHAM. W

DOUGLAS WILSON HALL.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,920,090 Lyonet al. July 25, 1933 2,336,512 Stroup Dec. 14, 1943 2,388,540 HartmannNov. 6, 1945 FOREIGN PATENTS Number Country Date 432,964 Great BritainAug. 2, 1935 132,612 Germany Apr. 5, 1901 OTHER REFERENCES "PracticalMetallurgy, published by the American Society for Metals, 1940, page 32.

Age Hardening of Metals, published by the American Society for Metals,1940, page 441.

